As a countermeasure to alleviate shortage of future frequency resources, secondary usage of frequencies has been discussed. Secondary usage of frequencies means that part of or all of frequency channels allocated to a certain system with a higher priority is secondarily used by another system. Generally, a system to which a frequency channel is allocated with a higher priority is called “primary system”, and a system that secondarily uses the frequency channel is called “secondary system”.
TV whitespaces are an example of frequency channels that are expected to be secondarily used. TV whitespaces mean frequency channels that are allocated to a TV broadcast system serving as a primary system but are not locally used by the TV broadcast system. By allowing a secondary system to use those TV whitespaces, efficient utilization of frequency resources can be achieved. There are a plurality of standards for wireless access schemes in a physical layer (PHY) and MAC layer for enabling secondary usage of the TV whitespaces, such as IEEE802.22, IEEE802.11af, and European Computer Manufacturer Association (ECM A)-392 (CogNea).
The IEEE802.19 working group has studied smooth coexistence of a plurality of secondary systems using different wireless access schemes. For example, in the IEEE802.19 working group, functions for coexistence of secondary systems are grouped into three function entities, i.e., a coexistence manager (CM), a coexistence enabler (CE), and a coexistence discovery and information server (CDIS). The CM is a functional entity for mainly making a decision for coexistence. The CE is a functional entity serving as an interface for mediating transmission of commands and exchange of information between the CM and a secondary usage node. The CDIS is a functional entity serving as a server for centrally managing information of a plurality of secondary systems.
For example, regarding those functional entities, Patent Literature 1 cited below discloses a technology in which a plurality of functional entities perform neighbor discovery in cooperation with each other.